Acrylate polymers and method of producing same



Patented Oct. 24, 1944 PATENT OFFICE ACRYLATE POLYMERS AND METHOD OFPRODUCING SAME Maxwell A. Pollack, Akron, Ohio, asslgnor to PittsburghPlate Glass Company, Allegheny County, Pa., a corporation ofPennsylvania No Drawing. Application August 2a, 1938, Serial No. 226,310

8 Claims. (Cl. 260-83) fusible polymeric unsaturated esters of acrylicand the alpha substituted acrylic acids and to the method of renderingsuch polymers infusible. Prior to. this invention, it has beenrecognized that certain methacrylic acid esters of unsaturated alcoholscould be polymerized to form infusible, insoluble products. Whilepolymers so produced have many desirable characteristics, they arediflicult to handle because of their lack of reactivity. Since they cannot be molded readily, the uses of these materials have been generallyconsidered to be limited to those applications wherein castpolymerization processes are permissible.

In accordance with my invention, I have been able to polymerizemonomeric unsaturated alcohol esters of the acrylic and alphasubstituted acrylic acids, such as allyl methacrylate, methallylchloracrylate, etc., under such conditions that a fusible polymer whichis soluble in organic solvents may be secured. This product may then bemolded to a convenient shape, if desired, and subsequently renderedinfusible by further polymerization in suitable manner, for example, byapplication of heat, light or other sources of energy with or Withoutcatalysts.

I have found that soluble, fusible polymers of the unsaturated esters ofthe acrylic and alpha substituted acrylic acids, such as allylmethacrylate, allyl chloracrylate, methallyl chloracrylate, methallylmethacrylate, etc., may be produced by polymerizing the monomeric esterunder proper conditions as hereinafter set forth. The fusible productsmay be produced, for example, by polymerization of the esters insolvents which are capable of dissolving the fusible polymer, andinterrupting polymerization before the infusible insoluble polymer isformed. Other methods whereby polymerization of the acrylate radicaloccurs without substantial interpolymerization of the unsaturated esterradical may also be resorted to. I have found that when the unsaturatedalcohol esters of acrylic or alpha substituted acrylic acids, such asallyl methacrylate, are polymerized in these solvents, for example,acetone, dioxane, chloroform, etc., a soluble polymer is formedinitially, but as polymerization proceeds, the insoluble polymer isproduced and the solution is converted to a non-reversible gel. Byinterrupting polymerization in a suitable manner before the gel isformed, a soluble, fusible polymer may be secured. This fusible polymeris found to be soluble in a majority of the solvents in which thepolymers of the saturated alcohol esters of acrylic acid or substitutedacrylic acids are normally soluble.

While the invention is especially applicable to the allyl or methallylesters of the acrylic or alpha substituted acrylic acids, 1 have foundthat desirable products may be secured from numerous other unsaturatedalcohol esters thereof. such as the crotyl, cyclohexenyl, oleyl, etc.,esters of these acids.

In general, it has been found that the solvents, in which polymers ofthe saturated alcohol esters of acrylic acid or alpha substitutedacrylic acid, such as methyl methacrylate, methyl chloracrylate, etc.,are soluble, should be used for this purpose. Thus, such solvents asacetone, dioxane, chloroform, toluene, benzene, carbon tetrachloride,methyl cellosolve acetate, phenyl cellosolve, dichloroethyl ether,xylene, tetralin,

dibutyl phthalate, etc., are found to be suitable.

In addition, the saturated acrylic or alpha substituted acrylic esterssuch as monomeric methyl, ethyl, propyl, etc.,- methacrylate orchloracrylate, or other polymerizable materials, for example. "vinylcompounds, such as styrene, vinyl chloride, vinyl acetate. etc., may beadded to the above solution before polymerization in order to formcopolymers. Since such materials particularly vinyl acetate, vinylchloride, styrene, etc., dissolve substantial amounts of the fusiblepolymers, they may be used themselves as solvents.

In each case, the polymerization should be interrupted before theinfusible product is produced. Since the polymer apparently becomesinfusible whenever the acrylate groups are interpolymerized with theunsaturated alcoholic group, polymerization should be interrupted beforethis phenomenon occurs. This may be ac: complished by stoppingpolymerization before gel formation is observed. In accordance with oneillustrative method of interrupting polymerization, the polymer may beseparated from the solvent by convenient methods, for example, by theaddition of a compound in which acrylate polymers are normallyinsoluble, such as methyl or ethyl alcohol, petroleum ether, water,ethylene glycol, etc. This process permits the isolation of the fusiblepolymer of the unsaturated alcohol ester of acrylic andalpha-substituted acrylic acids in a substantially pure state.

Polymerization may also be halted by lowering the temperature of thereaction mixture to a suitable degree, for example, to room temperatureor below. It has been found that although polymerization proceeds fairlyrapidly at temthen a hard,brittle iincreasing with increase oftemperature, it proceeds at such a slow rate that it may be practicallydiscontinued atv lower temperature. This is especially true whenpolymerization is carried out in solution. Y

In accordance with another effective method of interruptingpolymerization, inhibitors, such as pyrogallol, hydroquinone, aniline,phenylene diamine, sulphur, thiophenol, organic or inorganic salts orcomplexes of the reduced forms of metals infusible by suitable methodshereinafter more fully set fortla. I

It has been found that the yield of fusible-polymer appears to bedependent to a great extent upon the concentration ofthe monomer in thesolution undergoing polymerization. Thus, when very concentratedsolutions containing a large quantity, for example, in excess of 40430percent, of the monomeric allyl or methallyl methacrylate, are subjectedto conditions of polymerization, the amount of fusible polymer which maybe secured prior to gel formation is very low, often not in excess of 5percent by wei ht of the theoretical yield. Conversely, when solutionscontaining somewhat lower concentrations of monomer, for

example, up to 30 percent by weight, yields of the fusible polymerupward of 95 percent of the theoretical may be secured. Accordingly, itis preferred to deal with solutions having a monomer concentration below40 percent by weight. The yield of fusible polymer appears to beincreased by treating the solutions at increased temperatures andincreased catalyst concentrations. Thus, secured by polymerizing allylmethacrylate solutions at 100 C. or above than may be secured at 60 C.Catalystconcentrations up to 5 percent or more may be used in somecases. In general, conditions favoring the formation of-lower molecularweight polymers appear to result in increased yields of fusibleproducts.

. The following examples illustrate the prenata tion of these fusiblepolymers.

Example I One part by weight of allyl methacrylate was heated with 0.0!parts by weight of benzoyl peroxide and 5.6 parts by weight of acetoneunder reflux forA hours. The resulting solution was carefully poured,with stirring, into 100 parts of methanol. and soluble in acetone wasformed. This material began to soften when heated to 95-110" 0., and wasa soft plastic mass at 120140 G; How-' ever, prolonged heating causedloss of this plasticity, with the formation, first of an elastic, and

product.

Example 11 55 parts by weight of allyl chloracrylate were heated with 3parts by weight of benzoyl peroxide A white precipitate which wasfusible 2,801,055 'peratures of 35-40 C., or above, the reaction rateand 350 parts by weight of acetone at a temperature of 60 C. for 4hours. At this time, 300 parts of methanol were added to produceturbidity. and theresulting mixture was' poured slowly, with stirring,into 1600 parts of methanol. The white voluminous .precipitatethusformed was filtered and dried, and was soluble in acetone and chloroformand softened at 110425 0.

- It was a highly plastic gum at 140-150 C. hard- ,ehing with furtherheating.

- The fusible polymers so produced have many characteristics which aresimilar to those of the polymers formed from the saturated acrylic acidThey are soluble in such organic solvents as acetone, dioxane,chloroform, ethyl cellosolve acetate, triacetin, phenyl cellosolve,etc., and

soften upon heating. The allyl methacrylate polymer prepared in ExampleI softens and becomes readily plasticat a temperature of 95-110" C. Theallyl chloracrylate prepared in Example 11 softens at a temperature ofll0125 C. The

exact softening points of the products are dependent to a great degreeupon the temperature,

' catalyst concentration and monomer concentration of the solutionundergoing polymerization. In general, it is found that the chloracrylicesters soften at a temperature somewhat'higher than the correspondingacrylic and methacrylic esters and at normal temperatures are somewhatharder and more dense. All of these products appear to be easily moldedinto convenient shapes.

substantially greater yields may be In accordance with my invention, Ihave found that upon subjection of these polymers to heating attemperatures somewhat above the softening point thereof, for asuflicient period of time, they are converted into infusible, insoluble,transparent, hard and wear-resistant products. This conversion appearsto occur in the absence of catalysts. It may be assisted however, by theincorporation of usual polymerization catalysts, such as oxygen," ozone,air, peroxides, such as hydrogen peroxide, peroxide, basic or-a'cidiccatalysts, light, etc. By use of catalysts, it is found thattheconversion ,of these products to the infusible state may be securedat lower temperatures. The application of super-atmospheric pressure hasbeen found to assist the transformation to the insoluble and siblepolymeric allyl or methallyl infusible stage.

The properties of the products so produced are dependent to a degreeupon the conditions under which they were rendered infusible. Thus,extremely hard somewhat brittle products may be prepared by effectingthe treatment at relatively high temperatures or under high pressures.On the other hand, somewhat stronger, less brittle materials may besecured when the treatment is carried under moderate pressures andtemperatures sumcientlylow to permit a slow conversion of the fusiblepolymer into its infusible stage through a period in which it issubstantially completely molten.

By operation, in accordance with the present invention, it is thuspossible to form a molded article from the fusible polymer such as thefumethacrylate or chloracrylate previously referred to, and thereafterto render the molded product insoluble and infusible by heat. In thismanner, I am able to prepare transparent, hard, infusible moldedproducts which have many of the desirable properties of theconventionally known thermoplastic resins. By proper regulation of thepressure and temperature, the fusible polymer may be extruded benzoylperoxide or acetyl.

under such conditions that it becomes infusible as it leaves theextrusion die.

A large number of inert substances may be incorporated with the fusiblepolymer before subiecting to molding conditions. Suitable for suchpurposes are: fillers, such as wood-flour, mica, cotton flock, etc.,plasticizers, such as dibutyl phthalate, dicyclohexyl phthalate,triacetin, tricresyl phosphate, natural and synthetic resins, pigments,including titanium dioxide, carbon black, chromic oxide, lead chromate,etc., and organic dye-stuffs, such as methylene blue, methyl orange,etc. 1

If desired, similar products may be made from suitable copolymers of theolefinic esters of the acrylic or alpha substituted acrylic acids withthe saturated esters of these acids such as the methyl and ethyl estersthereof. found that infusible products which are stronger and lessbrittle than the single polymer may be produced in this manner. This isparticularly true when' the allyl or other oleflnic ester is polymerizedwith a saturated alcohol ester, such as the methyl or ethyl ester ofmethacrylic or chloracrylic acid.

The polymers whichI have prepared are capable of numerous uses, such asin lacquers, or other coating compositions, molded articles, safetyglass, etc. Where the composition is used for coating, it may be appliedin solution or in solid form, either alone or in combination withnatural or synthetic drying oils or resins and the like, the solventremoved and the coated article baked to render the surface infusible. Inthis manner, it ispossible to surface other polymers which are lessresistant to the action of solvents or of heat. When a coating of thefusible polymer of allyl methacrylate is deposited upon polymerizedmethyl methacrylate or similar polymer and the solvent removed, acoherent surfac thereof is formed. Upon heating the coated article tosuitable temperatures, this surface may be made transparent, hard andinfusible.

Being of the thermosetting type, these resins do not exhibit thephenomenon of cold flow," and are thus especially desirable for suchuses as airplane Windshields, where the pressure differences have beenfound to bow thermoplastic glass substitutes, particularly at the higheraltitudes. Coating may also be applied to metal, glass, wood, syntheticresins, etc., surfaces by extrusion of the heated fusible polymerdirectly on the suitably prepared surface. In similar manner, thesurface maybe heated and the polymer applied in powdered form, whereuponfusion occurs first to give a smooth, homogeneous film which may then beheat-hardened.

These resins are also suitable for many uses in the field of laminatedproducts. For example? products of great strength, elasticity andadherence may be secured by converting fusible allyl or methallylmethacrylate, chloracrylate, etc., into the infusible state in thepresence of a substantial amount of a compatible softening agent.Satisfactory non-shatterable glass sheets may be obtained by heating acombination of superposed sheets where the thermoplastic allylmethacrylate polymer and a softening agent such as dibutyl phthalate are,used as the adhesive layers It-has been found that these products areapplicable for impregnation purposes. Thus, leather, paper, wood orother comparatively porous substances may be steeped in a solution ofthe fusible polymer of methallyl methacrylate,

In some cases, it is,

Eram'ple m Two parts, of fusible allyl methacrylate polymer, preparedin. accordance with Example I, was rendered molten by heatingunder'slight pressure at 140 C. in a mold, and then converted to aclear, hard, infusible, and insoluble sheet by heating at 170 C. under apressure of 5000 lbs. per sq. in.,for one-half hour.

Example IV Two parts of fusible allyl chloracrylate polymer, prepared asin Example II, was fused at 140-150 C., and then molded as in ExampleIII at l60170 C. .under pressure of 2000 lbs. per sq. in. for one hour.The product obtained was hard, clear, and unaffected by solvents or heatto the point of pyrolytic decomposition.

Example V Two parts of the thermoplastic form of'allyl acrylate polymerwas fused at -140" C., and then heated in a mold at 160 C. under apressure of 3000 lbs. per sq. in. for one hour. The resulting productwas hard, clear, and unaffected by solvents or heat to the point ofpyrolytic decomposition.

Example VI One' part by weight of the fusible methallyl methacrylatepolymer was dissolved in 10 parts of acetone and the solution applied tothe surface of a cast sheet of polymerized methyl methacrylate. Uponevaporation of the solvent, a white opaque surface was obtained. Thisproduct was heated at -150 C. for one hour and a material having a,comparatively soft interior and a surface which was transparent, hard,and resistant to the action of heat and solvents was produced.

The process may also be extended to the production of mixed polymers orcopolymers. Thus, the fusible polymer prepared in accordance with myinvention may be mixed with other polymers such as polymers of methylmethacrylate, methyl chloracrylate, vinyl acetate, vinyl chloride,styrene, etc., and the mixture subjected to conditions ofpolymerization.

Although the present invention has been described with reference to thespecific details of certain embodiments thereof, it is not intended"that such details shall be regarded as limitations upon the scope ofthe invention except insofar as included in the accompanying claims.

I claim:

1. A method of polymerizing allyl methacrylate which comprisespolymerizing said ester, interrupting the polymerization aftersubstantial rupting the polymerization after substantial poly-'merization has occurred but before the polymer is converted into aninfusible gel, substantially completely separating residual monomer fromthe resulting polymer, subjecting the polymer to a temperature andpressure suflicient to ensure existance of the polymer in fused stateand con tinuing polymerization of the fusedpolymer for a time suflicientto convert the polymer into a substantially insoluble and infusiblestate.

3. A methodof preparing an insoluble, infusible resin from liminarilypolymerizing allyl acrylate, interrupting polymerization after it hasoccurred to a substantial degree, but before the polymer is convertedinto an infusible gel, substantially com pletely separating residualmonomer from the re sultins pfllymer, fusing the polymer by applicationof heat and pressure and continuing polymerization until the polymer isconverted into substantially infusible and insoluble state.

4. A method of preparing an infusible, insoluble resin from the ester of(a) acrylic acid and (b) a monohydric monounsaturated alcohol containing3 to 4 carbon atoms which uomprisespreliminarily polymerizing saidester, interrupting the polymerization after it has occurred to asubbefore the polymer is con-' stantial degree, but verted into aninfusible gel, substantially completely separating residual monomer fromthe resuiting polymer, fusing the polymer by application of heat andpressure and continuing polymerization until the polymer is convertedinto substantially infusible and insoluble state.

5. A method of preparing an infusible, insoluble resin which comprisespreliminarily polymerizing an ester of (a) methacrylic acid and (b) amonohydric monounsaturated alcohol containing 3 to 4 carbon atomsinterrupting the polymerization after it has occurred to a substantialdegree, butbeforethe polymer isconverted into an infusible gel,substantially completely separating residual monomer from-the resultilmpolymer, fusing and continuing polymerization until the polymer isconverted into substantially infusible and insoluble state.

6. A method of preparing an infusible, insoluble resin, which comprisespreliminarily polyallyl acrylate. which comprises premerizingan ester of(a) chloracrylic acid and (b) a monohydric, monounsaturated alcoholcontaining 3 to 4 carbon atoms, interrupting polymerization after it hasoccurred to a substantial degree, but before the polymer is convertedinto an infusible-gel, substantially completely separating residualmonomer from the resultin polymer, fusing the polymer by application ofheat and pressure and continuing polymerization until the polymer isconverted into substantially infuslble and insoluble state.

'7. A method of polymerizing an ester of (a) a monohydric alcohol havingan unsaturated linkage in an aliphatic chain of 3 to 4 carbon atoms and(b) an acid of the group consisting of acrylic acid, methacrylic acid,and chloroacrylic acid which comprises polymerizing said ester,interrupting the polymerization after substantial polymerization hasoccurred but before the polymer is'converted into an infusible gel,substantially completely separating residual monomer from the resultingpolymer, subjecting the polymer to a temperature and pressure suflicientto ensure 'existance of the polymer in fused state and continuingpolymerization of the fused polymer for a time sufiicient to convert thepolymer into a substantially insoluble and iniusible state.

8. The method of claim 1 in whichthe. polymerization is conducted in thepresence of a solvent for monomer and polymer.

mxwnma. POLLACK.

the polymer under heat and pressure

